At these doses of doxepin, dry mouth, an anticholinergic effect, was common (71%), and other side effects such as headache (25%), increased appetite (21%), and dizziness (21%) were also frequently observed, although these adverse effects were notably not significantly more frequent than with placebo in the study in question. In any case, taken together, higher doses of doxepin than very low doses are associated with an increased rate of side effects as well as apparent loss of hypnotic effectiveness with chronic treatment.Doxepin at a dose of 25 mg/day for 3 weeks has been found to decrease cortisol levels by 16% in adults with chronic insomnia and to increase melatonin production by 26% in healthy volunteers. In individuals with neuroendocrine dysregulation in the form of nocturnal melatonin deficiency presumably due to chronic insomnia, very-low-dose doxepin was found to restore melatonin levels to near-normal values after 3 weeks of treatment. These findings suggest that normalization of the hypothalamic–pituitary–adrenal axis and the circadian sleep–wake cycle may be involved in the beneficial effects of doxepin on sleep and insomnia. CYP2D6 inhibition
Doxepin has been identified as an inhibitor of CYP2D6 in vivo in a study of human patients being treated with 75 to 250 mg/day for depression. While it significantly altered metabolic ratios for sparteine and its metabolites, doxepin did not convert any of the patients to a different metabolizer phenotype (e.g., extensive to intermediate or poor). Nonetheless, inhibition of CYP2D6 by doxepin could be of clinical importance.
Acute intermittent porphyria (AIP) is a rare metabolic disorder affecting the production of heme resulting from a deficiency of the porphobilinogen deaminase. It is the most common of the acute porphyrias. Signs and symptoms
The clinical presentation of AIP is highly variable and non-specific. The patients are typically asymptomatic, with most gene carriers having no family history because the condition had remained latent for several generations. The syndrome marked by acute attacks affects only 10% of gene carriers. The mean age at diagnosis is 33 years old. Like other porphyrias, AIP is more likely to present in women. A distinguishing feature of AIP that separates it from other porphyrias is the absence of photosensitive cutaneous symptoms that occur in addition to acute attacks. Acute attacks
AIP is one of the four porphyrias that presents as an acute attack. 90% of affected individuals never experience an acute attack and are asymptomatic, while an estimated 5% of affected individuals experience repeat attacks. Attacks are most common in young adult women and are rare before puberty or after menopause. Severe acute attacks may require hospitalization. Patients usually experience symptoms in attacks that last from several hours to a few days. Between attacks, patients are asymptomatic.The most frequent presenting symptoms are abdominal pain and tachycardia. The abdominal pain is typically severe, colicky, poorly localized, and often associated with pain in back and legs. Patients may also present with vomiting and constipation, but diarrhea is unusual.