There are also mouth spray preparations of sildenafil for faster onset of action. Chemical synthesis
The preparation steps for synthesis of sildenafil are:
Methylation of 3-propylpyrazole-5-carboxylic acid ethyl ester with hot dimethyl sulfate
Hydrolysis with aqueous sodium hydroxide (NaOH) to free acid
Nitration with oleum/fuming nitric acid
Carboxamide formation with refluxing thionyl chloride/NH4OH
Reduction of nitro group to amino group
Acylation with 2-ethoxybenzoyl chloride
Cyclization
Sulfonation to the chlorosulfonyl derivative
Condensation with 1-methylpiperazine. History
Sildenafil (compound UK-92,480) was synthesized by a group of pharmaceutical chemists working at Pfizers Sandwich, Kent, research facility in England. It was initially studied for use in hypertension (high blood pressure) and angina pectoris (a symptom of ischaemic heart disease). The first clinical trials were conducted in Morriston Hospital in Swansea. Phase I clinical trials under the direction of Ian Osterloh suggested the drug had little effect on angina, but it could induce marked penile erections. Pfizer therefore decided to market it for erectile dysfunction, rather than for angina; this decision became an often-cited example of drug repositioning. The drug was patented in 1996, approved for use in erectile dysfunction by the FDA on 27 March 1998, becoming the first oral treatment approved to treat erectile dysfunction in the United States, and offered for sale in the United States later that year. It soon became a great success: annual sales of Viagra peaked in 2008 at US$1.934 billion.
Community-acquired pneumonia due to C. pneumoniae, H. influenzae, M. pneumoniae, or S. pneumoniae
Uncomplicated skin infections due to S. aureus, S. pyogenes, or S. agalactiae
Urethritis and cervicitis due to C. trachomatis or N. gonorrhoeae. In combination with ceftriaxone, azithromycin is part of the United States Centers for Disease Control-recommended regimen for the treatment of gonorrhea. Azithromycin is active as monotherapy in most cases, but the combination with ceftriaxone is recommended based on the relatively low barrier to resistance development in gonococci and due to frequent co-infection with C. trachomatis and N. gonorrhoeae. Trachoma due to C. trachomatis
Genital ulcer disease (chancroid) in men due to H. ducrey
Acute bacterial sinusitis due to H. influenzae, M. catarrhalis, or S. pneumoniae. Other agents, such as amoxicillin/clavulanate are generally preferred, however. Acute otitis media caused by H. influenzae, M. catarrhalis or S. pneumoniae. Azithromycin is not, however, a first-line agent for this condition. Amoxicillin or another beta lactam antibiotic is generally preferred. Pharyngitis or tonsillitis caused by S. pyogenes as an alternative to first-line therapy in individuals who cannot use first-line therapy

Bacterial susceptibility
Azithromycin has relatively broad but shallow antibacterial activity. It inhibits some Gram-positive bacteria, some Gram-negative bacteria, and many atypical bacteria. A strain of gonorrhea reported to be highly resistant to azithromycin was found in the population in 2015. Neisseria gonorrhoeae is normally susceptible to azithromycin, but the drug is not widely used as monotherapy due to a low barrier to resistance development.